1. Field of the Invention
The present invention is concerned with a surface graft material, a conductive pattern material, a metal particle pattern material, and a method of forming a graft pattern, a conductive pattern or a metal particle pattern.
2. Description of the Related Art
Surface modification of solid surface with a polymer can alter properties such as the wettability, stain resistance, adhesiveness, surface friction, and affinity for cells. Therefore, the surface modification has been widely studied in various industrial fields. Particularly, the surface modification with a surface graft polymer directly connected to a solid surface through a covalent bond has gathered attention. This is because the bond between the surface and the polymer is advantageously strong, the affinity of a graft polymer for a substance is different from the affinity of a polymer formed by a general coating and cross-linking method, and the graft polymer exhibits specific properties.
Applied technologies have been proposed which use the surface graft polymers having such advantages in various fields such as a field of living bodies (cell cultures, antithrombotic artificial blood vessels, artificial joints, etc.) hydrophilic films whose surface has to have high hydrophilicity, and hydrophilic supports of printing plates whose surface has to have high hydrophilicity. These applications utilize the specific properties of the graft polymers.
Furthermore, when such a surface graft polymer is formed in pattern, the specific properties of the graft polymer can be exhibited according to the pattern. Therefore, the graft polymers are used in fields of printing plate precursors, compartmentalized cultures and dye image formation.
For instance, it has been reported that a hydrophilic graft pattern is formed by using a polymerization initiating group (called “iniferter”) fixed on a surface, and used as a cellular compartmentalized culture material (Matuda et al. “Journal of biomedical materials research”, 53, 584 (2000)). It has also been reported that a dye is adsorbed by the graft pattern to form a visible image pattern (Matuda et al. “Langumuir”, 15, 5560 (1999)).
Furthermore, the following methods have been reported. One method comprises polymerizing a hydrophilic or hydrophobic monomer in pattern to obtain a polymer pattern by using an iniferter polymerization initiator fixed on the surface, and grafting a monomer having a dye structure to form a dye polymer pattern (A. T. Metters et al. “Macromolecules”, 36, 6739 (2003)). Another method comprises imagewise attaching an initiator onto a gold plate using a micro-contact printing method, causing an atom transfer polymerization (ATRP polymerization) from the initiator to form a graft polymer of HEMA (hydroxy ethyl methacrylate) or MMA (methyl methacrylate) in pattern, and using the obtained pattern as a resist (C. J. Hawker “Macromolecules”, 33, 597 (2000)).
According to these methods, the obtained pattern has a relatively low resolution at a level of 10 to 100 μm. However, generally, it has been difficult to form a pattern having higher resolution at a level of 0.10 to 10 μm. One of the reasons is considered as the following. These methods utilizes a surface graft reaction to generate graft polymers locally. Specifically, the methods comprise bringing monomers that generate grafts into contact with the surface of a base material, pattern-exposing the monomers to form graft polymers bonded to the base material in the exposed portions. However, at the exposure, free monomer molecules polymerize to form a large amount of homopolymers, which are bi-products, in addition to the formation of the graft polymers bonded to a substrate. These homopolymers are removed from the substrate by washing and the like. However, in the case of a fine pattern, it is difficult to completely remove the homopolymers present between the formed graft polymer patterns, and the resolution of the pattern is lowered.
Furthermore, the monomer used in the graft formation is generally in the state of a solution. Since the monomer is often harmful to the human body, it has been necessary to form a pattern in an environment equipped with a sufficiently powerful exhaust system.
Another proposed graft pattern forming method comprises providing an ablation polymer layer containing a photothermal conversion agent on a substrate surface, forming a graft polymer of a hydrophilic monomer such as acrylamide on the surface of the ablation polymer layer, causing ablation in the exposed areas by using an infrared laser, removing the graft polymer together with the ablation polymer to form a hydrophilic-hydrophobic pattern, and applying the pattern to a printing plate (Japanese Patent Application Laid-Open (JP-A) No. 11-119413). According to the method, there is no problem caused by the homopolymer during image formation. However, this method involves environmental problems such as diffusion of the decomposed products of the ablation polymer layer into the air. Moreover, it is hard to reduce the spot diameter of the infrared laser used in the pattern formation to 10 μm or less. Accordingly, it is difficult to form a fine pattern by the method.
As recited above, a pattern formation material and a pattern formation method have not been obtained which is capable of forming a polymer pattern with a high resolution at the level of 0.1 to 10 μm, and which are required for obtaining an effective surface modifying material and a highly functional material by modification of a solid surface with a polymer.
So far, various kinds of conductive pattern materials are used in the formation of wiring boards. Typical conductive patterns are formed by providing a conductive substance thin film prepared by a known method such as a vapor deposition method on an insulator, subjecting the conductive substance to a resist treatment, conducting a pattern-exposure, partially removing the resist, and conducting an etching treatment to form a desired pattern. The method includes at least four steps. When a wet etching is carried out, the waste liquid of the wet etching has to be suitably processed. Therefore, the method involves complicated processes (JP-A No. 2004-31588).
Another pattern formation method is known which involves use of a photoresist to form a conductive pattern material. The method comprises coating a base material with a photoresist polymer or attaching a photoresist on a dry film to a base material, exposing the photoresist with an arbitrary photomask to UV to form a pattern such as a lattice pattern. The method is useful for forming an electromagnetic wave shield which has to have a high conductivity.
The development of micromachines have progressed and ULSI (Ultra Large-Scale Integration) have been further downsized in recent years. Accordingly, a wiring structure thereof has to be fine at a nanometer level. The ability of the conventional metal etching to form fine wiring structure is limited and breaking of wire during processing of fine wires is likely to occur. Accordingly, there have been needs for a pattern formation method which is capable of forming a fine pattern whose orientation is controlled.
Further, various methods have been recently proposed which form patterns directly from digital data without using masks or the like. It is expected that fine patterns can be formed arbitrarily by using such methods. An example of such method uses a self-assembling monomolecular film. The method utilizes a molecular assembly which is spontaneously formed when a substrate is immersed in an organic solvent containing surfactant molecules. The combination of the material and the substrate may be, for instance, a combination of an organic silane compound and a SiO2 or Al2O3 substrate, or a combination of alcohol or amine and a platinum substrate. According to this method, patterns can be formed by the photolithography method or the like. Such monomolecular films enable to form a fine pattern. However, such a method is difficult to put into practice since the combination of the substrate and the material is limited. Accordingly, pattern formation techniques have not been developed which can be practically applied to form fine wiring.
In order to obtain a pattern material which is light, flexible, and friendly to the environment, organic transistors using a conductive polymer pattern have been studied. The supports comprising such organic materials are capable of easily forming (by a technique similar to printing at room temperature) an element which is light, thin, and flexible and which has a large area. Such features of the organic materials can be combined with electrical and optical characteristics of organic semiconductors which are under development. Such combinations are expected to enhance the development of a technology for the personalization of information, which is most strongly required in the present information technology. An example of the technology for the personalization is a technique of manufacturing wearable portable terminals with simple information processing functions and easily operable I/O functions. However, the technique has insufficient characteristics from the practical viewpoints of the durability, area expandability, stability in conductivity and productivity.
It has also been proposed to form a conductive pattern by using a highly hydrophilic graft polymer. An example of the methods comprises providing a hydrophobic compound in pattern on a surface having a hydrophilic graft polymer on its entire surface to form a hydrophilic-hydrophobic pattern, and attaching a conductive substance to hydrophilic graft regions (JP-A No. 2003-345038). Another example comprises forming a hydrophilic graft polymer on the entire surface of a base material, and attaching a conductive substance in pattern on the surface by inkjet or the like (JP-A No. 2003-234561). Another example comprises forming a graft polymer locally on the surface of a base material to form a hydrophilic graft polymer pattern, and attaching a conductive polymer to the hydrophilic graft portion (JP-A No. 2003-188498). All of these methods have an advantage that a pattern can be easily formed based on the digital data. However, the resolution of the pattern is insufficient. In the first and second examples, the resolution is limited at the process of attaching a conductive substance in pattern. In the third example, a graft polymer is locally formed by using a surface graft reaction. However, free monomers polymerize to form a lot of by-product homopolymers in addition to the formation of graft polymers bonded to a substrate during the formation of the graft polymer. If the pattern is fine, the homopolymers present among graft polymer patterns is hard to remove completely. Therefore, the resolution of the pattern is insufficient.
Not only a continuous metal thin film but also a fine metal particle pattern has attracted attention in which metal particles are adsorbed selectively to specific areas. In recent years, the society has become an advanced information society, and electronic devices have developed remarkably. In particular, the development of the computer technology supports the advanced information society. Factors which develop the computer technology include higher integration of semiconductor LSIs and a higher recording density of magnetic discs. In realizing the higher recording density of the magnetic disc, the defects in the magnetic layer has to be minimized and the smoothness of the layer has to be improved. In order to realize these objects, a film has been used in which metal particles having magnetic characteristics are dispersed on the surface of a base material. It is known that the recording capacity can be increased when the metal particles are patterned. Therefore, it has become important to dispose the metal particle adsorption region in pattern. The formation of the fine metal particle pattern for increasing the recording density also has problems similar to in the case of the metal thin film pattern. Accordingly, it has been difficult to form a metal particle pattern which is fine and which has a high resolution.